It now remains to be considered, how far there is reason to conclude that there had been sufficient degrees of compression in the mineral regions, for the purpose of melting the various substances with which we find strata consolidated, without changing the chemical constitution of those compound substances.

Had I, in reasoning a priori, asserted, That all mineral bodies might have been melted without change, when under sufficient compression, there might have arisen, in the minds of reasoning men, some doubt with regard to the certainty of that proposition, however probable it were to be esteemed:  But when, in reasoning a posteriori, it is found that all mineral bodies have been actually melted, then, all that is required to establish the proposition on which I have founded my theory, is to see that there must have been immense degrees of compression upon the subjects in question; for we neither know the degree of heat which had been employed, nor that of compression by which the effect of the heat must have been modified.

Now, in order to see that there had been immense compression, we have but to consider that the formation of the strata, which are to be consolidated, was at the bottom of the ocean, and that this place is to us unfathomable.  If it be farther necessary to show that it had been at such unfathomable depth strata were consolidated, it will be sufficient to observe, it is not upon the surface of the earth, or above the level of the sea, that this mineral operation can take place; for, it is there that those consolidated bodies are redissolved, or necessarily going into decay, which is the opposite to that operation which we are now inquiring after; therefore, if they were consolidated in any other place than at the bottom of the sea, it must have been between that place of their formation and the surface of the sea; but that is a supposition which we have not any reason to make; therefore, we must conclude that it was at the bottom of the ocean those stratified bodies had been consolidated.]

To conclude this long chemico-mineral disquisition, I have specimens in which the mixture of calcareous, siliceous, and metallic substances, in almost every species of concretion which is to be found in mineral bodies, may be observed, and in which there is exhibited, in miniature, almost every species of mineral transaction, which, in nature, is found upon a scale of grandeur and magnificence.  They are nodules contained in the whin-stone, porphyry, or basaltes of the Calton-hill, by Edinburgh; a body which is to be afterwards examined, when it will be found to have flowed, and to have been in fusion, by the operation of subterraneous heat.

This evidence, though most conclusive with regard to the application of subterraneous heat, as the means employed in bringing into fusion all the different substances with which strata may be found consolidated, is not directly a proof that strata had been consolidated by the fusion of their proper substance.  It was necessary to see the general nature of the evidence, for the universal application of subterraneous heat, in the fusion of every kind of mineral body.  Now, that this has been done, we may give examples of strata consolidated without the introduction of foreign matter, merely by the softening or fusion of their own materials.